Combustion control system



June 3, 1941; R. R. DONALDSON COMBUSTION CONTROL SYSTEM Filed April 25', 1938 3 Sheets-Sheet l 3 g 5 R ZVENTOR.

June 3, 1941. R. R. DONALDSON COMBUSTION CONTROL SYSTEM Filed April 25, 1938 3 Sheets-Sheet 2 f DINVENTOR.

June 4 R. R. DONALDSON ,243,944

COMBUSTION CONTROL SYSTEM Filed April 25, 1958 Sheets-Sheet 3 FM /E M BY ME Z ATIORNEYW- Patented June 3, 1941 COMBUSTION CONTROL SYSTEM Robert R. Donaldson, Pittsburgh, Pa., asslgnor to John M. Hopwood, Mount Lebanon, Pa.

Application April 25, 1938, Serial No. 204,051

1 Claim.

This invention relates to control of combustion in steam boilers, and it is an object of this invention to provide a method of controlling combustion and a system that will automatically control combustion in accordance with variations in steam pressure and in accordance with variations in the load on prime movers supplied with steam by the boilers.

In the operation of steam boiler plants, such for example as steam-electric plants and especially large plants where a number of steamdriven alternator units are involved, it is the practice to operate the most eflicient of these units at all times at its maximum efliciency, the other units being used as stand-bys to take care of peak loads. Changes in the load on the alternators do not immediately result in changes in steam pressure, and for this reason, where combustion is controlled only from steam pressure or some function of steam pressure, a substantial change in steam pressure may at times occur before any change in the rate of combustion is efiected.

In accordance with this invention, combustion in the various boiler furnaces is controlled from variations in the steam pressure and from variations in load on the alternators that are driven by prime movers supplied with steam by the boiler. The procedure involves the measuring of the steam pressure and the trend in steam flow to the prime movers and then adjusting the rate of combustion in accordance with the joint measurement of steam pressure variations and trend in steam flow.

The trend in steam may be obtained by measuring the load on a prime mover supplied with steam, and where the load is an electric alternator or generator, the load may be determined by measuring the kilowatt output of the alternator or generator. In cases where the prime mover utilizes all the steam supplied to it, then the load output of the alternator will be a measure of the steam flow; but when the prime mover is amultiple stage turbine and steam is bled from one of the low pressure stages, then the measurement of the load on the generator may not represent the total steam flow to the turbine, but it does represent the trend or change in rate of steam flow, because the amount of steam bled off is usually only a small part of the total steam delivered to the turbine. In any case, the invention is applicable to either situation as measurements of changes in trend in steam flow as well as actual steam flow are sufllciently accurate when used in connection with measurements of steam pressure to provide accurate and rapid in dications of the requirements for combustion.

The control system is so arranged that the combustion is controlled automatically to maintain a substantially constant steam pressure. When changes in load on the alternator occur, such load change is measured and utilized to effect an immediate change in the rate of combustion. The rate of combustion is caused to change until an equilibrium or balance between steam pressure and rate of steam generation, and the actual load on the prime movers, is reached. The system operates also to eifect a change in combustion rate in case there is a change in steam pressure without a change in load on the prime mover.

It is, therefore, an object of this invention to provide a system that will control combustion both from variations in steam pressure and from load on the steam-operated prime movers.

Other objects of the invention will, in part, be apparent and will, in part, be obvious from the following description taken in conjunction with the accompanying drawings in which:

Fig. l is a diagrammatic view of a steam boiler and alternator provided with a control system embodying the invention.

Fig. 2 is an enlarged view of a regulator utilized in the control system, three such regulators being shown in Figure 1, one of them operating the outlet or uptake damper, another controlling the rate of fuel feed, and the third controlling the rate of combustion air supply;

Figs. 3 and 4 are views in section of the devices utilized in the control system, the one in Fig. 3 responding to load changes on the alternator to effect through a master regulator a change in the combustion rate; and the one in Fig. 4 responding to combustion chamber pressure to control the rate of air supply regulator;

Fig. 5 is a view in section of a diaphragm-operated valve shown in Fig. 1;

Fig. 6 is a fragmentary view of me pilot valve operating mechanism for the regulator shown in Fig. 2, the view being taken in the direction of lines VIVI of Fig. 2;

Fig. 7 is an enlarged view in longitudinal section of a regulator shown in Fig. 1; and

Fig. 8 is an enlarged view in longitudinal section of a fixed but adjustable orifice embodied in the control system of Fig. 1.

Throughout the drawings and the specification like reference characters indicate like parts.

In Fig. 1 of the drawings, there is illustrated a boiler furnace I supplying steam to a turbine 2 which drives an electric alternator 3. The particular furnace illustrated is arranged to be fired with coal or other solid fuel, fed by means of a stoker 4 driven by an adjustable-speed motor 5, such as an electric motor. The speed of motor 5 is controlled by means of a field rheostat 6 which is adjusted by a regulator "l. The air for combustion may be supplied through a duct 8 by a forced draft fan i5 and the rate of air supply may be regulated by means of a damper it operated by a regulator It in accordance with changes in pressure in the combustion chamber of the furnace. The air supply regulator is controlled by a regulating device i2 which responds to the pressure in the combustion chamber of the fur nace. This regulator is shown in detail in Fig. 4 of the drawings. The furnace may be operated with either induced or natural draft as the control system will function with either one.

The furnace draft is controlled by means of a damper 63 located in the outlet or uptake 14 of the furnace and this damper is operated by a regulator hi which is controlled by a regulating device it such as shown in Fig. 4 which in turn is controlled by a master regulator H. The master regulator operates in accordance with, as well as jointly and singly, in response to the steam pressure in steam header i3 and the load on the alternator 3.

In connection with the steam turbine, shown in Fig. 1, it will be understood that the steam valve indicated diagrammatically at is is controlled by a speed responsive device indicated diagrammatically by numeral 29, to maintain constant speed of operation.

The master regulator H operates to effect simultaneous adjustment in the outlet damper I3, and therefore in the draft, and in the rate of feed of fuel in response either to a change in the steam header pressure, or to a change in the load on alternator 3, or in response to a change in the steam pressure and load on the alternator. The load on the alternator is measured by a regulator 2| such as shown in Fig. 3, and this regulator operates on the master regulator I! to cause it to effect a change in the draft and the rate of fuel feed as required by the load on the alternator.

The air supply rate regulator l l operates dampor iii in such fashion that a substantially constant pressure is maintained in the combustion chamber of the furnace. Device i2 responds to these changes whether caused by excess air being supplied by the forced draft fan or by a change in combustion pressure resulting from a change in position of the outlet damper or by a change in draft for any other reason, and causes regulator 9 to adjust damper i c to the position required for the maintenance of the pressure desired in the combustion chamber of the furnace.

Regulators 1, l l, and 15 are illustrated as being of the same construction or type and for this reason the regulator shown in Fig. 2 will be a sufiicient illustration of each so far as details of construction and operation are concerned. Also, regulators i2 and i5 are of the same construction and only one detailed illustration thereof is necessary and this is shown in Fig 4.

Device l6 responds to the pressure existing in a pipe 22 between a diaphragm-operated valve or orifice 23 and a fixed, but adjustable orifice 24. One end of pipe 22 is connected to the out-let of the furnace at a point behind or upstream from, the outlet damper l3 and the other end is connected through valve 23 to the atmosphere. A

change in the setting of valve 23 causes a change in flow through pipe 22 from the atmosphere into the uptake of the furnace. This flow is proportional to the rate of delivery of combustion air for a given setting of valve 23 and damper l3. If the setting of the valve is changed or if the draft changes, the flow through pipe 22 changes whereby the pressure (in this case suction) between valve 23 and orifice 24 varies, causing device 16 to transmit a control impulse to regulator 15. Regulator l5 responds to this impulse and changes the position of damper l3 until device I8 is in balance or equilibrium with the pressure between orifice 24 and valve 23.

The suction at the uptake of the furnace may vary over a relatively wide range and may, in some cases, reach a value of 15 inches of water or more. By employing a fixed orifice 24 in the position indicated and an adjustable valve 23, device It will function throughout its full operating range on a pressure variation range of only a fraction of the range of variation in suction occurring at the uptake of the furnace. Device I6 causes regulator IE to operate in such fashion that for all practical purposes a substantially constant pressure is maintained between valve 23 and orifice 24.

For each and every position of valve or orifice device IE will cause the regulator l5 to assume a definite, but different, position. In other Words, regulator 45 will shift the outlet damper [3 throughout its full operating range in response to valve 23 being shifted throughout its full operating range. As the load on the boiler increases, regulator IT causes valve 23 to open whereby the pressure between the valve and the orifice tends to approach atmospheric pressure. As this pressure rises, device l6 responds, transmitting a control impulse to regulator 15, and causing the damper to open Wider. As the outlet damper opens wider the flow through pipe 22 increases. As this flow increases, regulator I6 will continue to adjust regulator l5 until the outlet damper has been adjusted to a position required by or corresponding to the particular setting of valve 23. The outlet damper will come to rest when the pressure between valve 23 and the fixed orifice 24 reaches a value at which regulator i6 is placed in a state of balance or equilibrium. In case the steam pressure or the load on alternator 3, or a combination of a change in steam pressure and load on the alternator, requires a decrease in the rate of combustion, master regulator l'l causes valve 23 to be moved toward closed position, thereby reducing the flow through pipe 22 and increasing the suction acting on the diaphragm of device 16. This change will cause regulator 15 to move the damper 53 toward closed position. It will continue to move the damper toward the closed position until the pressure between valve 23 and the orifice 24 corresponds to a value at which device I8 is again in balance. When device [6 is in balance, the outlet damper !3 will be in a position corresponding to the particular draft required by the setting of valve 23.

Master regulator l1 comprises an escapement valve 25, a beam or lever 26 fulcrumed on a knife edge 2?, for operating the valve to control the magnitude of pressure impulses sent from a supply pipe 28, having air therein at constant pressure, to a sending line 29 serving valve 23 and regulator I. Regulator I! also comprises a pressure responsive member 30, such as a bellows, dis-posed within a pressure tight housing 31, and which is operatively connected to lever 26 by a push rod 32 having a knife edge 33 hearing against the lower side of the lever at a point relatively close to fulcrum 21. Bellows 30 is made of a strong, corrosive resistant steel alloy and is subject to the pressure of the steam in steam header 1, the interior of housing 3| being connected to the steam header by a pipe 3|. The lever 26 is urged in a clockwise direction as shown in Fig. 1 by a spring 35 one end of which is connected to a stem 36 having at its upper end a knife edge 31 bearing on the upper side of the lever. The other end of the spring is secured to a nut 33 having threaded engagement with an adjusting screw 39 by means of which the pull of the spring on the lever may be adjusted to any desired value. Screw 39 is rotatively supported in a tubular member 39 carried by the frame of regulator |1.

Regulator I1 also includes a pressure responsive member 40, such as a bellows, which is disposed within a pressure tight housing 4|. This bellows is operatively connected to lever 26 by means of a push rod 42, having at its free end a knife edge 43 bearing on the upper side of the lever at a point to the right of fulcrum 21--i. e, on the same side of the fulcrum that plunger 32 acts on the lever.

Pressures are transmitted to housing 4| by regulator 2| in accordance with the load on. the alternator 3. The effect of the pressure transmitted to housing 4| is to cause bellows 40 to impose such a loading on lever 26, as will cause the master regulator to effect substantially the same adjustment in the supply of fuel and air to the furnace that would have been brought about by a change in the steam pressure in the header l8. For example, if the load on alternator 3 should increase, the loading which the bellows 40 would impose on the master regulator l1, would be the same as if a reduction in steam pressure had immediately taken place in steam header l8. By producing this effect on master regulator l1, the supply of fuel and air to the furnace is increased immediately when an increase in load on alternator 3 takes place, whereby there will be substantially no time lag between a change in the load on alternator 3 and a change in the rate of combustion.

In order that responses of the master regulator |1 either to a change in load on the alternator 3 or in steam pressure in the steam header |8, shall not overcorrect the rate of combustion a dash pot device 44 is provided and operatlvely connected to lever 26. Dash pot 44 comprises a bellows 45 disposed in a pressure tight housing 46, which bellows is.- urged toward its extended position by means of a spring 41. Housing 45 is connected to sending line 29 so that bellows 45 is subjected to the sending pressure. The dash pot also includes a cylinder 48 in which a piston 49 is disposed and connected by a spring 50 to the lever 26. Cylinder 48 is provided at its upper end with an overflow chamber which is connected to the interior of bellows 45 by means of a by-pass 52 having a needle valve 53 therein. The by-pass is connected to the overflow chamher at a point well above, and to bellows 45 at a point well below, piston 49. The bellows and cylinder contain a fluid, such as oil, so that when the bellows is compressed, the piston will move upwardly, compressing spring 50 and causing it to act upwardly on lever 26. As the pressure on the bellows persists, oil fiows from below the piston through the by-pass to the overflow chamber 5|, therebyigra'du'ally wiping" out the effect of the pressure of the fluid acting on the piston and causing the piston to return gradually to its normal or free position. If bellows expands because of a reduction in the pressure transmitted to housing 46, the effect will be to cause the piston 49 to move downwardly in its cylinder. This tends to elongate spring and thereby exert a downward pull on lever 26. This downward pull diminishes and finally becomes zero, or substantially so, as fluid flows from overflow chamber 5| through the needle valve into the space below piston 49.

Escapement valve 25 comprises a valve body 55 having at its lower and upper ends tapered valve seats 56 and 51, the upper valve seat being formed in a fitting 58 threaded into the upper end of the valve body for adjustment purposes. The valve also includes a plug 59 having tapered surfaces at its opposite ends disposed to cooperate with valve seats 56 and 51 to control, in accordance with its position with respect to such valve seats, the magnitude of the pressure existing within the valve body and transmitted to sending line 29.

Valve plug 59 is urged toward upper valve seat 51 by a spring 60 disposed between a flange 6| on the plug and the lower end of the valve body. Valve fitting 58 as shown on drawings, is hollow so that the interior of the valve body is vented to the atmosphere. Through this passage, a stem on the upper end of plug 59 extends and contacts with a reach link 63, the upper end of which engages an adjustable screw 64 supported by a yieldable member 65 secured to the adjacent end of lever 26. Spring 60, by urging valve plug 59 upwardly, also urges the reach link into positive contact with the adjustment screw 64.

When valve plug 59 moves toward the inlet valve seat 56, it moves away from exhaust valve seat 51, thereby reducing the pressure within the valve body to a value approaching atmospheric value, depending upon the closeness of the valve plug to inlet valve seat 56. As the valve moves toward exhaust valve seat 51, the rate of escape or leak-off of air to the atmosphere is reduced, thereby causing the pressure within the valve body and in sending line 29 to increase. When the exhaust port is completely closed, the value of pressure within the valve body and that sent to the sending line is a maximum and equal to the pressure available in. the supply pipe. When the valve is seated on the inlet seat, then the pressure within the valve body will be reduced to atmospheric as the air within the sending line and within the valve body will exhaust to the atmosphere. This will be the minimum pressure established in the valve body and the sending line. Depending upon the relative position of plug 59 with respect to the exhaust port 51 and the inlet port 56, the pressure within the valve body and that transmitted to the sending line may be varied from the minimum to the maximum values in infinite steps or increments.

The pressure sent from the sending line 29 to valve 23 and regulator 1 is also transmitted to housing 46 containing dash pot bellows 45; therefore, it will be apparent that the force exerted by the dash pot on the bellows in opposition to that exerted on lever 26 by the steam pressure responsive bellows as well as the loading bellows 40 will vary with the magnitude of the pressure sent out to the sending line by the escapement valve. Also, the greater the pressure transmitted to the dash pot bellows, the greater will be the rate of flow through the needle valve. The greater the flow through the needle valve, the greater will be the tendency for the dash pot to relieve its effect on the master regulator ll, although the retarding effect at the instant the sending pressure is applied to the dash pot bellows will be greater as the sending pressures increase. The needle valve is so adjusted that when the master regulator responds to a change in steam pressure or turbine load, the combustion control apparatus will have sufficient time in which to respond before the master sends out an impulse requiring further adjustments in combustion. ihis, therefore, prevents over or underregulation.

Device 2! is shown in detail in 3. This device responds to the actual load imposed on the alternator 3 and therefore in efiect responds to variations in the flow of steam to turbine 2.

Device 2!, therefore, measures any change in the trend of steam flow to the turbine, because when the load on the alternator increases, more steam must be delivered to the turbine; or if the load on the alternator decreases, the flow of steam must also decrease. If all the steam supplied to the turbine were used in driving the alternator, the response of device 2! to changes in load on the alternator would be a measure of the total rate of steam fiow to the turbine.

Since in large power plants, steam is sometimes bled from the turbine, all of the steam is not utilized in developing power, i. e. all the steam is not utilized in developing electric power through the alternator which it drives. However, the amount of steam bled away is for all practical purposes, only a small portion of the total amount of steam delivered to the turbine. In any case, device 2! will measure the trend in steam flow whether that trend be upward or downward.

Device 2i comprises an escapement valve such as valve 25 shown and described in connection with master regulator [1, therefore corresponding parts will be designated by corresponding reference characters primed. The escapemerit valve is operated by a lever or beam 61, one

end of which is iulcrumed on a knife edge 58, and the other end of which is connected to a tension or loading spring 69. The upper end of spring 69 is connected to a screw 10, having threaded engagement with a nut "II for initially adjusting the tension in the spring. Nut H is supported on a tubular member l2 secured to the frame of the device. Spring 69 urges lever 61 in a clockwise direction, thereby tending to move valve member 59 toward inlet port 56' to reduce the pressure within the valve body and in sending line 13. Lever El is connected by a yoke i3, having a knife edge i l bearing on the upper side of the lever, to a connecting rod 15. The lower end of rod '55 carries an electric coil winding 16. This winding is provided at its center with a disc '11 of non-magnetic material which is secured to rod 15. The lower end of rod 15 carries a relatively long spring 78 which is connected to a bellows '19 disposed within a housing 80 to which pressure is transmitted from sending line '53. Bellows i9 is urged towards its expanded position by a strong spring 8 i.

Device 2i also includes a coil winding 82 supported by and secured to a support plate 83. Coils 16 and 32 are energized by alternator 3 in such manner that the value of force developed by their magnetic fields will be proportional to the load on the alternator. One of these coils is energized in accordance with the current output of the alternator and the other is energized in accordance with the voltage thereof. As indicated by Figs. 1 and 3, coil 16 is connected to a current transformer 84 and. coil 82 is connected to a voltage transformer 85. Escapement valve 25 is so designed and adjusted that the range of pressure impulses delivered to sending line 13 and to housing 38 may vary over a range from atmospheric pressure to say 60 pounds per square inch for full travel of the valve plug 55?. Since the pressures in housing 00 will vary over the operating range of the valve, spring 6i must be so designed that it can withstand the force of this pressure and at the same time keep he deflection or compression of bellows 79 within its range of deflection when the pressure in housing 89 varies between atmospheric and its maximum pressure, say 60 pounds per square inch.

Since the valve of pressure in line 13 and housing 80 is dependent upon the position of valve plug 59' which in turn is dependent upon the position of coil winding i5, spring 78 must exert such a force on coil 76 for any value of power developed by alternator 3 that the movement of this coil in either direction will exert a force tending to move valve plug 59 in accordance with a direct or straight line function of the power developed by the alternator.

Thus if it is assumed that when alternator 3 is at no load, the pressure in housing and in line 13 will be at atmospheric value and that when the alternator is at full load or at some particular value above full load, the pressure in housing 80 and in line l3 will be at the maximum pressure that may be transmitted by valve 25, then for any increase in load on alternator 3 the force exerted by coils 82 and 16 on rod 15 will be a function of this load. For each increase in load on alternator 3 the pressure in housing 80 will increase. Thus as the pressure in housing 85] increases spring 78 will exert an ever increasing force opposing downward movement of coil 16, and the more the load increases, the greater will be the force exerted by spring 18. If valve plug 59' has a maximum travel of say 0.01 inch between exhaust port seat and inlet port seat, the increasing forces exerted by spring '18 caused by compression of bellows 19 will be such that coil 16 will move downwardly the amount required to move valve plug 59 through 0.01 inch over full load range of the alternator.

From the above it will be seen that the maximum air gap between coils l6 and 82 over full range operation will be so small that it will not alter the accuracy of its operation at any point within its full range movement; therefore, device 2| will be caused to transmit a pressure impulse into sending lin T3 that is substantially a linear function of the load on alternator 3 for all values of load.

A relatively small movement of coil 76 is sufficient to move the escapement valve plug 59 through its full working stroke; 1. e., the travel required to move the valve from a closed inlet port position to a closed outlet port position. The length of this stroke may be as little as 0.01 inch. When such a short stroke is involved, coils 1'6 and 82 will always be so close together that the force developed thereby and applied to rod 15 will be substantially a linear function of the power output of the alternator. Because of the relatively small movement of these coils, the air gap between remains so constant that a change in the gap does not affect the accuracy of the device. For this reason the pressur 1m pulses delivered by valve 25' bear a linear relationship to the load on the alternator,

As the load on the alternator increases, rod I is pulled downwardly, causing the escapement valve 25' to increase the pressure of the air impulse delivered to bellows housing 80 and to the bellows housing 4|. This increased pressure in housing H of master regulator II causes lever 26 to turn on its fulcrum in the same direction that it would have turned had the steam pressure in header I8 decreased, whereby the rate of combustion is increased. The rate of combustion will continue to increase until the steam pressure is raised to a value that will put regulator I'I back in balance at which time the combustion rate will remain stationary at some particular value until another change in combustion rate is required, as indicated either by a change in steam pressure on the boiler or by a change in load on the alternator 3, or both. If the load on the alternator decreases, the opposite action takes place. When the alternator load decreases rod I5 moves upwardly, whereby the inlet port of valve 25' is reduced, thereby reducing the pressure in bellows housing II of the master regulator II. This decrease in pressure on bellows 40 reduces the loading on the master regulator and produces an efifect corresponding to that which would have occurred had the boiler steam pressure increased. The master regulator therefore responds and through valve 23 and regulator I, causes the control system to decrease the rate of combustion until the demand for steam is met. When the master regulator has effected the required reduction in the rate of combustion, the regulator will be in balance again when the steam pressure has been lowered to some value where it balances the loading imposed by bellows 40.

The construction of devices I2 and I 8 is shown in Fig. 4. This regulator is substantially the same in construction as device 2I except that instead of moving the escapement valve by means of coils I6 and 82, the escapement valve is operated by a pressure responsive diaphragm 86 located in a diaphragm chamber 86'. Diaphragm 86 is connected by a link 81 to a. yoke I3 which is suspended by a knife edge I4 on the lever 81 and connected to spring I8 by a link 90. The points where links 81 and 90 pass out of the diaphragm chamber are sealed by means of sealing-diaphragms 9| and 92. These sealing diaphragms are secured to the diaphragm housing and to the links in pressure-tight relationship thereto.

Devices I2 and I6 are connected to respond to the pressure in the combustion chamber of furnace I and to the pressure between valve 23 and fixed orifices 24, respectively. As to device I2, the lower side of the diaphragm is connected to the combustion chamber by means of a pipe 93; and as to device IS, the lower side of the diaphragm is connected by a pipe 94 to pipe 22 at a point between valve 23 and orifice 24. The opposite sides of these diaphragms are open to atmospheric pressure so that they deflect in accordance with the difference between atmospheric pressure and the pressure existing either in the combustion chamber of the furnace in the case of device I2 or to the pressure in pipe 22 in the case of device I0. Device I2 is adjusted to maintain a substantially constant pressure in the combustion chamber of the furnace.

Whenever the position of outlet damper I3 is changed, a change occurs in the pressure in the combustion chamber. In response to such change, device I2 causes regulator II to shift damper I0 to a position that will allow such flow of air to the furnace from fan 9 as will restore the combustion chamber pressure to the value desired. If damper I3 is opened more and more, damper I0 is opened more and more, or if damper I3 is moved toward closed position then damper 9 is moved toward closed position. In this manner the combustion chamber pressure is maintained substantially constant and the rate of flow of air to the furnace is regulated to conform to the requirements for combustion because damper I3 is adjusted in accordance with the demand for steam under the control of master regulator II.

Valve 23 is shown in Fig. 5 and comprises a valve body 96, having a valve plug 91 therein. The valve plug is shaped like an inverted cup and is formed with a plurality of ports 98 in the skirt thereof. The valve plug is carried by a plunger 99 to which it is adjustably secured. The plunger extends upwardly into a bonnet I00 and is provided with a thrust plate IOI at its upper end against which a. diaphragm I02 works. The diaphragm is secured between a flanged ring I02 carried by the bonnet and a cap I03 which is connected to impulse line 29. The valve is urged toward open position by a spring I04.

When the boiler is operating at full load the pressure acting on diaphragm I02 will be at a minimum and the valve plug will be in its open position, and when the boiler load is off, this valve will be in substantially closed position because the pressure on diaphragm I02 will be at a maximum. The valve will occupy intermediate positions for intermediate boiler loads.

As the pressure impulses acting on diaphragm I02 increase, because of decreasing demand for combustion, the valve will move toward closed position and the diaphragm of device I6 will move downwardly, causing increasing pressure impulses to be delivered to regulator I5. These increasing impulses cause regulator I5 to move upwardly to shift damper I3 toward closed position and decrease the furnace draft. The opposite action takes place when the diaphragm is subjected to decreasing impulses, as this indicates a need for a higher rate of combustion. As valve 23 opens, the diaphragm of device I6 moves upwardly, thereby reducing the pressure impulse sent to regulator I 5 in response to which it shifts damper I3 toward open position and increasing the furnace draft.

The construction and operation of regulators 1, II, and I5 is illustrated by the detailed drawing shown in Fig. 2. Each of these regulators comprises a cylinder I05 in which a piston I06 is working. The piston is provided with a piston rod I01 that extends upwardly through the upper head of the cylinder, and carries at its upper end a crosshead I08 from which side rods I09 and H0 depend. These side rods extend downwardly along the sides of the cylinder and are connected at their lower ends by a crosshead III.

' Pressure for operating the piston in either direction is admitted from a supply pipe H2 and the direction of its admission, 1. e. whether it is admitted at the upper or the lower end of the cylinder, is controlled by a pilot valve II3 operated by a, diaphragm H4. The upper side of the diaphragm is subjected to control impulses delivered thereto either from sending line 29, from escapement valve 25' of regulator I6 or from the escapement valve 25' of device I2 as the case may be. The valve plug II 5 of the pilot valve is connected to the diaphragm by means of a rod H5, the upper end of which bears against a thrust plate l l8 associated with the diaphragm. Between this thrust plate and a moveable collar or socket H9 is a spring i2G which tends to move the diaphragm and the valve upwardly.

Socket H9 is carried by a bell crank I21 which is pivotally supported on a pin I22 journalled in a bracket I23 secured to the cylinder. The upwardly extending arm of the bell crank carries a roller I24 which operates on a cam or compensating bar I25 secured to side rod HQ. This bar is inclined at such an angle and cooperates with bell crank to always move the pilot valve plug H in a direction opposite to that in which it is moved in response to a change in pressure on diaphragm H4 and towards off or neutral position.

When the pilot valve is moved downwardly as a result of increasing pressures being transmitted to the diaphragm, pressure is admitted to the lower end of the cylinder, causing the piston to move upwardly. As the piston moves upwardly, bell crank l2| turns in a clockwise direction, causing the pilot valve plug H5 to be moved upwardly toward its neutral or off position. If a greater impulse is transmitted to the diaphragm, the pilot valve is again moved downwardly, causing the piston to move still further upwardly and, when it has moved a predetermined distance, ca-m bar I25 actingon bell crank it! shifts the pilot valve to or toward neutral position. The opposite action takes place if the pressures acting on the diaphragm are decreasing. In such case, spring I28 moves the pilot valve upwardly, causing operating pressure to be admitted to the upper side of the piston whereby it moves downwardly. As the piston moves downwardly, spring I acting on bell crank l2! causes it to follow the cam bar I to return the pilot valve to neutral position. In this fashion, step by step movement of the piston is effected in either direction in accordance with the magnitude of the pressure impulses acting on the diaphragm. The construction and opera tion of the regulator shown in Fig. 2 including the pilot valve mechanism are shown and described in United States Letters Patent 2,044,936 dated June 23, 1936.

In accordance with this invention combustion in a boiler furnace supplying steam to prime movers such as steam turbines connected to drive electric generators, is controlled in accordance with the'demand for steam by measuring the steam pressure, measuring the load on the steam turbine and then regulating combus tion in accordance with either and/or both measurements to insure that the proper rate of steam generation will be maintained. This is accomplished by providing apparatus for supplying fuel and air to the boiler furnace and adjusting the furnace draft, and utilizing a master regulator which responds both singly and jointly to variations in steam pressure and load on the prime mover to effect the necessary operation of the apparatus for adjusting the draft, the feed of fuel, and the supply of air for combustion. In this manner, combustion rates are adjusted to follow, with a minimum time lag, the demand for steam.

The specific control system illustrated c0mprises master regulator H which operates directly to effect adjustments in the draft and the feed of fuel accompanied by adjustment in the air supply, and device or meter 2| which loads the master regulator in accordance with the load on alternator 3, and therefore the load on turbine 2, to cause the master regulator to respond and effect an immediate increase in the combustion rate, in case the load increases, instead of waiting for a drop in boiler steam pressure to occur, or to cause the master regulator to effeet a decrease in combustion, in case the turbine load decreases, without Waiting for the steam pressure to rise.

Where the load on the alternator remains constant, regulator l'l responds to changes in steam pressure to regulate combustion, but its operation is modified by the loading imposed thereon by device 2| and bellows 49.

Having thus described the invention, What I claim as new and desire to be secured by Letters Patent is:

Apparatus for controlling combustion in steam boiler furnaces supplying steam to a prime mover connected to drive an electric alternator comprising apparatus for regulating the furnace draft, apparatus for regulating the rate of fuel delivery to the furnace, means for transmitting variable control impulses to the furnace draft apparatus and the rate of fuel delivery apparatus, means responsive to steam pressure for actuating said impulse transmitting means, and means responsive to the load output of the alternator for actuating said impulse transmitting means, said load and steam pressure responsive means acting jointly to cause adjustment in the rate of combustion to continu until a balance is reached between steam pressure and load output of the alternator.

ROBERT R. DONALDSON. 

